Liquid membrane separation, which combines the steps of solvent extraction and stripping in a single process, is an area generating special interest because of its potential for low cost and energy savings. There are two types of liquid membrane systems: supported liquid membranes, immobilized on a porous polymeric membrane; and liquid surfactant membranes as a (water/oil)/water emulsion or a (oil/water)/oil emulsion.
Supported liquid membranes (SLM) generally consist of a solvent/carrier mixture which is contained within the pores of the polymeric solid, i.e., the membrane. Into this solvent/carrier impregnated membrane, a solute from a feed solution is selectively removed by combining with the carrier to form a complex. This complex diffuses through the membrane and is then stripped from the carrier at the other side of the membrane.
A supported liquid membrane is most typically used for the extraction of metal ions and consists of a solution of an organic solvent containing the carrier (an extractant), the solution being contained within the pores of a porous polymeric support or membrane. The membrane is interposed between two aqueous solutions, a feed solution containing the metal ions to be extracted and a stripping solution for recovering the extracted ions. By adjusting the pH or other chemical potential gradient between the feed solution and the stripping solution, a driving force is provided and the metal ions extracted from the feed solution are transported through the membrane and transferred into the stripping solution. Previously, one problem with SLM's has been that while selective extraction and effective transport can be accomplished, SLM's have had limited lifetimes as the extractant in the organic solution of the membrane is continuously lost into the aqueous phase. This continuous loss of extractant has naturally hampered the application of SLM's to industrial processes.
Accordingly, it is an object of this invention to provide a supported liquid membrane including a microporous polybenzimidazole membrane containing an extractant mixture within the membrane pores for use, e.g., to separate metal ions, e.g., aluminum, antimony, arsenic, bismuth, cadmium, chromium, copper, cobalt, gallium, gold, hafnium, indium, iridium, iron, lead, manganese, mercury, molybdenum, neodymium, nickel, niobium, osmium, palladium, platinum, rhenium, rhodium, ruthenium, selenium, silver, tantalum, tellurium, thallium, thorium, tin, tungsten, uranium, vanadium, zinc or zirconium, from an aqueous solution.
Another object of this invention is to provide a supported liquid membrane apparatus including a feed compartment, and a stripping compartment, said compartments separated by a microporous polybenzimidazole membrane containing an extractant mixture within the membrane pores.
Still another object of this invention is to provide a process of selectively removing metal ions from aqueous wastewater streams such as those that result from, e.g., hydrometallurgical operations.